In recent years it has been found that decaying radium in the ground beneath buildings has been releasing radon gas into the building through the basement floor. This problem can be solved by venting the basement by means of a fan and thus removing the radon present in the basement. Up to this time the apparatus used for this process has included a fan placed in line with a pipe which extends from beneath the basement floor and through the side wall of the basement. The fan draws radon from beneath the floor through the pipes to the outside air. This is satisfactory, to some extent, if the fan is sealed and if the pipes are sealed to prevent radon from leaking into the basement after it is pulled from beneath the basement floor. However, leaks develop and such systems are thus not completely satisfactory.